7+ C# Prime Number Checker Program Examples

This post contains a total of 7+ Hand-Picked C Sharp Prime number checker Program Examples with Source Code. All these prime number checker programs are made using C Sharp Programming Language.

You can use the source code of these examples with credits to the original owner.

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C Sharp Prime Number Checker Programs

1. By Zarthah

Made by Zarthah. C# Program to Check if numbers in a given range are prime or not, the program by default checks the numbers in range 10 – 100. Source

If its 'true' it means its a prime number
-10 = False
-9 = False
-8 = False
-7 = False
-6 = False
-5 = False
-4 = False
-3 = False
-2 = False
-1 = False
0 = False
1 = False
2 = True
3 = True
4 = False
5 = True
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


namespace SoloLearn
{
    class Program
    {
        static bool prime(int num)
        {
            if(num > 1)
            {
                if(num == 2)
                    return true;
                
                for(int i = 2; i <= num/2; i++)
                {
                    if(num % i == 0)
                        return false;                                   
                }
                return true;         
            }
            return false;
        }
        static void Main(string[] args)
        {
            Console.WriteLine("If its 'true' it means its a prime number");
            
            // For example, we will check from -10 to 100, which those numbers are the prime number.
            for(int i = -10; i <= 100; i++)
            {
                Console.Write(Convert.ToString(i));
                Console.Write(" = ");
                Console.WriteLine(prime(i));
            }
        }
    }
}

2. By Canny

Made by Canny. A simple program to check if a Number is PRIME or NOT A PRIME NUMBER. Source

10
10 is NOT A PRIME NUMBER
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SoloLearn
{
    class Program
    {
        static void Main(string[] args)
        {
            double num, divisor = 1, counter=0;
            
        num = Convert.ToInt32(Console.ReadLine()); 
        
        do
        {
            if(num % divisor == 0) 
            {
            
                counter++; //counts the factors
                divisor++; 
            }
            else
            divisor++; 
        }
        
        while(divisor<=num); 
        
        if(counter==2) //TRUE if the number has two factors
        Console.Write($"{num} is a PRIME NUMBER");
        else
        Console.Write($"{num} is NOT A PRIME NUMBER");
        }
    }
}

3. By Samuel Kurnas

Made by Samuel Kurnas. Source

7
7 is prime number
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


namespace SoloLearn
{
	class Program
	{
		static void Main(string[] args)
		{
			//insert some number
            int number = Convert.ToInt32(Console.ReadLine());

            if (isPrimeNumber(number))
                Console.WriteLine(number + " is prime number");
            else
                Console.WriteLine(number + " is not prime number");
		}
		
		public static bool isPrimeNumber(int number)
        {
            if (number == 1)
                return false;

            if (number == 2)
                return true;

            int loops = Convert.ToInt32(Math.Floor(Math.Sqrt(number)));

            for (int i = 2;i<=loops;i++)
            {
                //modulo
                if (number%i == 0)
                    return false;
            }

            return true;
        }
	}
}

4. By ermain F

Made by ermain F. Prime number checker program that takes an arbitrary integer and determines whether it is prime. Source

The number you entered is 12
12 is not a prime number
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


namespace Integers
{
    class PrimeNumbers
    {
    
   static bool isAPrime( int numba)
    {
     int factor =0;
        for (int loop=1; loop<=numba; loop++){
            if ( numba % loop == 0)
            factor++;
        }
            
        if (factor == 2)
        return true;
      
      return false;   
    }
    
        static void Main(string[] args)
        {
        Console.WriteLine("Prime Number Checker version 1.0.0\nCode By Germain.F..................\n\n");
       Int32 number=Convert.ToInt32( Console.ReadLine());
        Console.WriteLine ("The number you entered is {0}", number);
        
        if ( isAPrime(number) )
        Console.WriteLine ("{0} is a prime number", number);
        else
        Console.WriteLine ("{0} is not a prime number", number);

        Console.WriteLine("\n.......................Please don't forget to leave a like or a comment.\nThanks for testing!");
            
        }
    }
}

5. By Mikeul

Made by Mikeul. Source

9
9 is not a prime number
using System;
namespace Prime
{
    class Program
    {
        static void Main(string[] args)
        {
            int input = int.Parse(Console.ReadLine());
            if(input.IsPrime())
                Console.WriteLine($"{input} is a prime number");
            else
                Console.WriteLine($"{input} is not a prime number");
        }
    }
    public static class Count
    {
        public static bool IsPrime(this int n)
        {
            if(n < 2)
                return false;
            for(int i = 2; i <= n/2; i++)
                if(n % i == 0)
                    return false;
            return true;
         }
     }
}

6. By Domagoj Puljiฤ‡

Made by Domagoj Puljiฤ‡. Source

3
Number is prime.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


namespace SoloLearn
{
    class Program
    {
        static void Main(string[] args)
        {
            int n=Convert.ToInt32(Console.ReadLine());
            if(isPrime(n)){
               Console.WriteLine("Number is prime.");
            }
            else {
               Console.WriteLine("Number is not prime.");
            }
        }
        static bool isPrime(int number)
        {
           if(number==1 || number==0){
              return false; 
           } 
           for(int i=2;i<=Math.Sqrt(number);i++){
              if(number%i==0){ 
                  return false;
              }
           }
           return true;
        }
    }
}

7. By Damon Keane

Made by Damon Keane. A simple C Sharp program to see if the input number is prime or not. Source

15
Not Prime
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SoloLearn
{
    class Program
    {  
    public static void Prime(int n) {
    bool prime = true;
           
               int x = Convert.ToInt32(Math.Sqrt(n));
           if(n == 1)  
           {
               prime = false;
           }
           for(int i = 2; i <= x; i++)
           {
               if(n%i == 0)
               {
                   prime = false;
               }
           } 
        if(prime)
        {
            Console.WriteLine("Is Prime");
        }
        else {
            Console.WriteLine("Not Prime");
            }
           }
        static void Main(string[] args)
        {
        int num = Convert.ToInt32(Console.ReadLine());
        Prime(num);
       } 
    }
}

8. By Divi

Made by Divi. Enter any integer ( not more than 32bit) and the program will tell if the number is prime or not. Source

19
19 is a prime number.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SoloLearn
{
    class Program
    { 
        static void Main()
        {
        int x;
x = Convert.ToInt32(Console.ReadLine());
int result = PrimeCheck(x);
if (result==0)
{Console.WriteLine("{0} is not a prime number.",x);}
else {Console.WriteLine("{0} is a prime number.",x);};}

static int PrimeCheck(int x)
{
for(int y=2;y<x;y++)
{if(x%y==0)
{return 0;}}
return 1;}}}